Magazines for use with semi-automatic firearms that use rim fire cartridges typically utilize some variation of one or two cartridge stacking arrangements. One typical arrangement of cartridges is a straight stack in which the rims of the cartridges are configured against a vertical end wall of the magazine. Another typical arrangement is the "banana clip" in which the rims of the cartridges are configured against an arcuate (banana) shaped end wall of the magazine.
An example of the straight stack arrangement is disclosed in U.S. Pat. No. 4,509,283 to Chesnut, in which vertical front and rear end walls of the magazine hold rim fire cartridges in a single straight stack. In such an arrangement, the first cartridge loaded into the magazine contacts a spring-loaded follower. The follower has a top surface formed at an angle relative to horizontal which approximately matches an angle between a longitudinal axis through the magazine well of the firearm relative to vertical. For example, if the angle between the longitudinal axis through the magazine well and vertical is 30 degrees, the angle of the follower surface and each cartridge therein relative to horizontal is also approximately 30 degrees. By matching the cartridge angle to the magazine well/vertical angle, a cartridge is effectively placed in a plane generally parallel to a plane passing through a longitudinal center line of the firearm chamber.
To allow a vertical arrangement of cartridges, it may be required to provide a loading assist knob on the follower. The knob is attached to the follower and passes through a slot in one of the sidewalls of the magazine. To load the magazine, the knob is engaged to depress the follower downwardly into the magazine as cartridges are inserted through an open top end thereof. Without the knob, frictional forces between the front and rear end walls of the magazine and the cartridges as well as the force from the follower spring tend to make it very difficult, if not impossible, to load more than a few cartridges into the magazine.
If the magazine well/vertical angle is varied, for example, to 20.degree., the vertical arrangement of cartridges tends to become impractical. However, it has been found that a 20.degree. well/vertical angle provides a subjectively more natural aiming relationship of the firearm at the end of an extended human arm. When cartridges are placed in a vertical front and rear end wall magazine, having a follower angle of 20.degree., in a similar manner as per the '283 patent referenced above, the frictional forces between the cartridges and the front and rear end walls of the magazine may create upfeed problems which make the magazine inoperative after several rounds. Thus, to reduce the frictional forces the cartridges must be stacked in a different fashion to remove contact between the cartridges and the front or rear end wall.
Examples of a second format arrangement are disclosed in U.S. Pat. Nos. 4,672,760 and 4,790,094, both to Chesnut et al. In the '760 and '094 patents, the "banana" or arcuate shaped rear end wall of the magazine takes advantage of the curved stacking shape of the cartridges. The cartridges may also be stacked in a "nested" arrangement forming a double curving column of cartridges. Such curving is caused by the increased rim diameter as opposed to the casing diameter of each cartridge. Additionally, it is necessary to ensure that the rim of each cartridge is in front of the next cartridge rim directly below. Without this rim arrangement, jams occur when the uppermost cartridge is attempted to be loaded into the firearm chamber, as is well-known in the art. By nesting cartridges and curving the magazine, more cartridges may be loaded into a magazine than can be loaded into a non-curving single straight stack magazine. Still, it is a requirement of the arcuate shaped magazine that at least the uppermost cartridge be positioned at an angle relative to horizontal that approximately matches the magazine well/vertical angle of the firearm.
The banana clip may not require a thumb knob on the follower to assist in loading of the magazine. The forces generated between the cartridges and the magazine tend to be more rearward than forward, and thus the cartridges do not ride on both the front and rear end walls. Therefore, frictional forces are less in the banana clip magazine than in the vertical end wall magazine and loading is correspondingly easier. The banana clip style magazine, however, is not generally suited to a semi-automatic handgun that receives the magazine through the handgrip thereof, as a handgrip magazine well generally requires a magazine having vertical end walls which are straight and parallel to each other. Thus, there is a need for a magazine which takes advantage of the reduced frictional forces of a curved banana clip magazine and yet is adapted for insertion into the straight magazine well of a pistol.